How tVNS works: what happens in your tragus

Step 1: The clip

Your tragus

This is your tragus: the small flap of ear in front of your ear canal. It is where the clip sits, and where every pulse goes.

Keep scrolling and the model will follow. Drag sideways on it to turn it.

Step 1: The clip

A branch of the vagus nerve

The yellow line is the auricular branch of the vagus nerve, drawn as if you could see through the skin. In many people it reaches the skin on the ear-canal side of the tragus, as well as the hollow of the ear.

Step 1: The clip

The clip

The clip grips the tragus from both sides. Its round body sits on the outside and a slim arm reaches just inside the ear canal, so there is a pad on each side. The nerve runs underneath.

Step 2: The slice

Slice through the tragus

Now cut across the ear at the level of the pads and lift the top away, so you can look down on the cut. Scroll slowly to watch it happen.

Step 2: The slice

Inside the tragus

Between the two pads are skin, a thin layer of fat and a plate of cartilage. A little gel fills the gap between each pad and the skin.

Step 2: The slice

Nerve fibres in the skin

The yellow dots are vagus nerve fibres in the skin facing the ear canal. The grey dots are other skin nerves on the outer side. Nerve supply varies from person to person.

Step 3: The pulse

The pulse

Each pulse pushes a tiny current in through one pad, across the tragus and out through the other, then straight back the other way, so no charge is left behind. Most of it crosses straight between the pads.

Step 4: The tingle

The tingle

The current does not travel along the nerve. It nudges the nerve endings in the skin under the pads, and when the nudge is big enough an ending fires. That is the tingle you feel.

In many people some of the endings on the ear-canal side belong to the vagus nerve, which carries their signals back towards the brainstem. Turn the strength up and more endings join in.

Step 5: The skin

Why the skin matters

Most of the push is needed just to get through the thin outer layer of the skin. Dry skin resists far more than skin with gel on it, so the device has to raise its voltage to keep the current the same. If it reaches its limit, the current falls short and fewer endings fire.